Stackable plastic trays

ABSTRACT

In various embodiments of the present invention, trays with mechanical separation features are provided that reduce the adhesion between adjacent trays in a stack of at least partially nested trays or other plastic products. The separation features formed in the trays are strategically located to reduce contact between one tray&#39;s bottom surface from the top surface of the tray beneath it. In various embodiments, this is accomplished by employing a plurality of different tray designs, e.g., “A design” and “B design.” The different tray designs have substantially the same size and contour except for the location of the separation features. To prevent adhesion between the trays when stacked, the different tray designs are alternated when stacked (e.g., A design, B design, A design, B design) and the separation features reduce the nesting depth of adjacent trays.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/314,359, filed Mar. 16, 2010, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

Various embodiments of the present invention relate to plastic products with improved stackability.

BACKGROUND OF THE INVENTION

Certain thermoplastic materials exhibit high degrees of surface cohesiveness. When these thermoplastics are fabricated into various finished products such as medical trays for disposable instruments, the products produced from these thermoplastics may adhere to each other as the products are nested together at the end of the fabrication process. As used herein, the terms “products” and “trays” may be used interchangeably.

The high degree of surface cohesiveness exhibited by many thermoplastics results in formed trays, which have been “nested” together to reduce the total volume of space required for storage and shipment, become adhered together due to the cohesive properties of their mating surfaces. For some materials with especially high levels of surface cohesiveness such as Polyethylene Terephthalate Glycol copolymer (PETG) and Amorphous Polyethylene Terephthalate (APET), the trays will adhere to one another with such force that the effort required to separate them can result in damage to the trays and in some cases the effective destruction of the tray.

Previous techniques and methods employed to prevent this undesired phenomena have had limited success and introduce other problems. These techniques include negative draft angle de-nesting lugs and/or the use of chemical release agents applied to the surface of the thermoplastic material prior to the fabrication process. Other less conventional techniques include applying chemical release agents to the surface of the finished tray prior to nesting the trays together.

A common problem with conventional de-nesting lugs is reduced manufacturing efficiency because the de-nesting lugs have a “negative draft angle.” Typically, for a formed tray to be successfully extracted from a mold, a significant percentage of the geometry of the tray and likewise the mold upon which it was formed, must exhibit what is conventionally known as “positive draft angle.” A positive draft angle is the geometry of the finished plastic tray where the tangential relationship of vertical features of the tray to a horizontal plane across a common base of the tray is greater than 90°.

However, as noted above the geometry of a de-nesting lug has a “negative draft angle.” The “negative angle de-nesting” lug's geometry is such that as viewed in a cross-sectional perspective, the top of the de-nesting lug overhangs the bottom of the de-nesting lug, which has a similar profile to that of a stream bank where the current has eroded the soil from beneath the top of the bank. In conventional molding, the material which is formed into the profile under the “river banks edge” must deflect and bend out of the way of the portion of the mold that creates the “overhang” as the plastic product is removed from the mold.

As noted, the material which has had to deflect in order to pass by the “overhang” then needs to snap back to its original geometry. In some cases, this geometry of the de-nesting lug may be destroyed in the de-molding process if the profile is overly aggressive in its degree of negative angle and/or relative size. In addition, if too many de-nesting lugs have been formed into the finished tray, the tray may be destroyed due to the sheer force required to extract the tray from the mold even if any given de-nesting lug by itself would not have resulted in damage.

Another much rarer methodology for creating the geometry of the de-nesting lug requires that the portion of the mold that creates the “overhang” on the river bank profile of the de-nesting lug has the ability to retract out of the way prior to de-molding the tray. Actuated mold geometry for plastic trays manufactured for disposable end-use applications, such as medical trays, deli trays, etc., is extremely rare due to the added cost, complexity and maintenance requirements of such mold tooling. But even in circumstances where the negative economic impact of such complex tooling could be justified, frequently the required finished geometry of the plastic tray itself makes such an approach incompatible with the functionality of the finished product.

Another disadvantage to the use of “negative degree” de-nesting lugs is the unintended locking effect that can occur on a stack of plastic trays when a downward force has been exerted on the stack of trays. In this case, the base of the de-nesting lug can deflect and bypass the overhanging ledge of a de-nesting lug on an adjacent tray. When this type of event occurs, the “de-nesting lug” in one tray snaps into the de-nesting lug of an adjacent tray thereby effectively creating a “locking lug.” The force required to separate trays in this condition often far exceeds the force that would have been required if the lugs had not otherwise been molded into the product.

The other predominantly employed technique for mitigating the inherent surface cohesion properties of molded plastic products is the use of topical release agents. The predominant chemical used for this purpose is silicone. The silicone release agent is typically applied to the top of the plastic sheet after the sheet has exited the last set of calendaring rollers during the sheet film manufacturing process. The silicone may be applied via several techniques including aerosol spray, mechanical applicators, and bath dipping. The application of the silicone release agent is an inexact science at best. The amount of silicone applied, its consistency and degree of coverage across the plastic sheet, and the consistency and performance of the chemical agent itself are all highly variable factors. This variability can create negative results in the finished tray.

Also, the vast majority of all plastic sheets which are used to make medical trays enter the forming process as continuously coiled roll. These rolls are typically shipped and stored on end, with the core of the roll oriented substantially perpendicular to the support surface. Even if the topical application of the silicone is consistently applied, the effects of gravitational pull can cause the silicone to gravitate downward on the surface of the coiled plastic rolls such that over time there can be a noticeable accumulation of silicone on the lower portion of the plastic roll. When this material is then processed into finished plastic trays, the amount of silicon present across the tray can vary greatly.

Some manufacturers of plastic sheets have attempted to reduce the variability inherent in the topical application of silicone by adding release agents into the formulation of the plastic sheet. These internal release agents propagate to the surface of the sheet; however, the efficiency of this solution has not been proven and the negative impact of release agents on the surface of the finished tray still exist.

The medical industry often uses plastic trays to package individual items for use by medical professionals. Medical device manufactures typically sterilize the trays, place items in the trays and then enclose the item within the tray by applying a lid that seals against the tray. A typical process for a tray destined for the medical industry is generally outlined in the following paragraphs.

A tray may be manufactured by thermoforming or other process utilizing thermoplastic sheet materials such as PETG or APET which have been topically treated with a release agent such as silicone. In some cases, these trays may also include negative angle de-nesting lugs. After the trays are manufactured, they are typically nested together, bagged, boxed and eventually transported to a medical device manufacturer.

The trays are initially warehoused by the medical device manufacturer until they are needed. When needed for production, the trays are removed in bulk from their shipping containers and passed into a clean room where the components which are to be placed into the trays reside. Line operators will separate a tray from its associated stack and then load a product into the tray.

The next step is the placement of a lid over the open surface of the tray to enclose the product within the tray. The lid engages a flange that extends around the periphery of the tray. The lid may be constructed of a number of different materials with the most commonly used material being a porous fabric-like material produced from high density polyethylene fibers such as DuPont's Tyvek®. The lid is typically gas permeable, but its structure is such that while gases may pass through, bacteria and viruses cannot.

The tray and lid may then be bonded together proximate the flange area through a process known as heat sealing. A die applies pressure, sandwiching the two materials together while heat is applied uniformly across the surface by the die. The heat may be produced by one or more techniques including but not limited to conduction, electrical impulse and radio frequency energy. The amount of heat or pressure applied and the duration of the process varies depending on the materials being used, the geometry of the tray and other factors such as the amount of release agent applied to the trays.

The presence of a topical release agent on the surface of the tray can negatively affect the integrity of the seal. The heat sealing process must overcome the release agent in order to produce a bond that will ensure the sterile integrity of the package post sterilization. Due to the previously discussed variability inherent to the application of these topical release agents, the medical device manufacturer can experience unpredictable variations in the quality of their sealing process. This variation in the amount and consistency of the application of the topical release agent manifests itself into variability in the integrity of the seal. As a result, the manufacturer may experience higher inspection costs requiring destructive testing of sealed trays and an increased risk of field failures and product recalls.

Accordingly, there is a need in the industry for improved tray designs that discourage adhesion of adjacent trays when stacked.

BRIEF SUMMARY OF THE INVENTION

In general, embodiments of the present invention provide plastic products with improved stackability.

In one aspect of the invention, a stack of plastic trays is provided. The stack of plastic trays includes a first tray and a second tray. The first tray includes a substantially planar flange portion extending around the perimeter of the first tray, a first contour portion inward of the flange portion and configured to receive a product, and a plurality of first separation features formed within the first contour portion and having a positive draft angle. The second tray includes a substantially planar flange portion extending around the perimeter of the second tray, a second contour portion having substantially the same shape as the first contour portion, and a plurality of second separation features disposed within the second contour portion of the second tray and having a positive draft angle. The location of the plurality of second separation features relative to the second contour portion is different from a location of the plurality of first separation features relative to the first contour portion. Additionally, the first tray is disposed on top of the second tray and each one of the plurality of first separation features engages a portion of the second contour portion of the second tray at a location spaced apart from the second separation features formed in the second contour portion thereby spacing apart a bottom surface of the first contour portion of the first tray from the top surface of the second contour portion of the second tray.

In another aspect of the invention, a plurality of stacked trays is provided. The stack of trays includes a first tray having a first contour defining a plurality of walls that at least partially define a pocket to receive a product and a first plurality of separation features formed in at least some of the plurality of walls. The plurality of stacked trays also includes a second tray having a second contour defining a plurality of walls wherein the plurality of walls defined by the second contour have the same relative position as the plurality of walls defined by the first contour, and the second contour further defining a second plurality of separation features formed in at least some of the plurality of walls of the second tray at different relative locations from the first plurality of separation features defined in the first tray. The first tray is disposed on top of and partially nested within the second tray and each one of the plurality of first separation features engages a portion of the plurality of walls defined by the second contour at a location spaced apart from the second plurality of separation features.

In a further aspect of the invention, a method of producing a stack of plastic trays is provided. This method includes the steps of: forming a first tray having a first contour defining a plurality of walls that at least partially define a pocket to receive a product and a first plurality of separation features formed in at least some of the plurality of walls; forming a second tray having a second contour defining a plurality of walls wherein the plurality of walls defined by the second contour have the same relative position as the plurality of walls defined by the first contour, and the second contour further defining a second plurality of separation features formed in at least some of the plurality of walls of the second tray at different relative locations from the first plurality of separation features defined in the first tray; and disposing a first tray on top of the second tray wherein each one of the plurality of first separation features engages a portion of the plurality of walls defined by the second contour at a location spaced apart from the second plurality of separation features.

In another aspect of the invention, a plurality of stacked trays for use in storing medical devices is provided. The stack of medical trays includes first tray comprising a substantially planar flange portion extending around the perimeter of the first tray and configured to provide an engagement surface for a lid to seal, a first contour defining a first plurality of walls that at least partially define a pocket to receive a medical device, and a first plurality of separation features formed in at least some of the plurality of walls. The stack of medical trays also includes a second tray comprising: a substantially planar flange portion extending around the perimeter of the first tray and configured to provide an engagement surface for a lid to seal, and a second contour defining a second plurality of walls. The second plurality of walls have the same relative size and position within the second contour as the first plurality of walls defined by the first contour, and the second contour further defines a second plurality of separation features formed in at least some of the plurality of walls of the second tray at different relative locations from the first plurality of separation features defined in the first tray. The first tray is disposed on top of and partially nested within the second tray and each one of the plurality of first separation features engages a portion of the plurality of walls defined by the second contour at a location spaced apart from the second plurality of separation features. Additionally, the engagement of the first separation features of the second contour spaces apart other bottom surfaces of the first contour from the top surfaces of the second contour thereby discouraging adhesion between the first and second trays in the stack of trays.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1 is an isometric view of a plastic tray 100 according to an embodiment of the present invention.

FIG. 2 is an isometric view of a plastic tray 200 according to an embodiment of the present invention.

FIG. 3 is an isometric view of a stack of plurality of plastic trays according to an embodiment of the present invention.

FIG. 4 is a side view of the stack of plastic trays shown in FIG. 3.

FIG. 5 is a top view of the stack of plastic trays shown in FIGS. 3 and 4.

FIG. 6 is a cross-section view of a portion of the stack illustrated in FIG. 5 through section A-A.

FIG. 7 is an enlarged view of portion B of the stack of trays illustrated in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

In various embodiments of the present invention, trays with mechanical separation features are provided that reduce the adhesion between adjacent trays in a stack of at least partially nested trays or other plastic products. The separation features formed in the trays are strategically located to reduce contact between one tray's bottom surface from the top surface of the tray beneath it. In various embodiments, this is accomplished by employing a plurality of different tray designs, e.g., “A design” and “B design.” The different tray designs have substantially the same size and contour except for the location of the separation features. To prevent adhesion between the trays when stacked, the different tray designs are alternated when stacked (e.g., A design, B design, A design, B design) and the separation features reduce the nesting depth of adjacent trays.

In certain embodiments, the separation features are ribs/notches positioned within the contours of the tray design. The ribs/notches may be strategically located as not to interfere with the end use of the tray. For example, the separation features may be positioned so as to avoid sealing surfaces or to avoid interference with a component subsequently stored in the tray. Additionally, a plurality of separation features may be distributed throughout the tray to provide a stable support surface when the trays are stacked. The size and shape of the separation features can vary between different applications depending on the contour of the tray necessitated by the purpose of the tray. The height of the separation features can also be varied to achieve a desired nesting depth of adjacent trays.

Generally described, using different geometries between adjacently stacked trays reduces the contact area between the adjacent trays thereby reducing the adhesive force between the adjacent trays. In some embodiments, the different geometries create relatively small contact points between adjacent trays where the rest of the surface area of the top tray is suspended just above that of the tray beneath. By properly engineering the location and relative depth or height of the separation features, the trays may partially nest one into another while also reducing adhesion between the trays.

FIG. 1 illustrates a first tray 100 having a contour configured to hold an item. The tray 100 may be manufactured from Polyethylene Terephthalate (PETE), Polyethylene Terephthalate Glycol copolymer (PETG), Amorphous Polyethylene Terephthalate (APET), or other plastic material.

In various embodiments, the tray 100 is manufactured using a thermoforming process. In the thermoforming process, a sheet of thermoplastic material is heated to a temperature at which it becomes suitably pliable for forming over or into a mold. The heated plastic sheet is drawn over or into the mold through the application of vacuum draw (e.g., vacuum forming), air pressure (e.g., pressure forming), and/or mechanical application of a mating mold which matches the geometry of the form mold (e.g., plug assist). Any and or all of these techniques may be employed during the forming process of the thermoplastic sheet to form the tray 100.

Generally described, the molding process extracts the latent heat from the thermoplastic sheet until a set point is reached whereby the thermoplastic sheet has cooled enough so that when the sheet is removed from the mold it retains the shape of the mold on which it was formed. Post forming, the excess sheet outside of the perimeter of the desired finished dimensions of the formed part may be removed. The removal of this excess material can be achieved through a cutting press using a steel rule die, a matched metal die, a forged die or other type of die in which downward pressure is employed to drive a sharp metal construct through the plastic sheet thus freeing the desired finished tray from the excess plastic.

The contour of tray 100 includes a series of peaks 110 and valleys 120 of differing heights (and depths) that create pockets configured to receive an item. The relative height difference between the peaks 110 and valleys 120 can create walls 130 within the contour to define the item pockets. Some of these walls 130 may also support the item to be placed within the tray 100.

The illustrated tray 100 also includes a substantially planar flange 140 that extends outwardly around the periphery of the tray 100. In various embodiments, this flange 140 may be used in downstream operations to provide a surface for engagement by a lid or seal (not shown). Other embodiments may not include this flange.

In some embodiments, significant portions of the surface area of the tray 100 are planar (either tops of peaks 110 or bottoms of valleys 120). This type of surface may create adhesion issues if a tray 100 is nested with another tray 100.

Separation features 150 may be formed in some of the peaks 110, valleys 120 and/or walls 130. In the illustrated embodiment, the separation features 150 are notches formed at strategic locations within the walls 130. In the illustrated embodiment, four separation features are formed in the tray. However, other embodiments may have more of less separation features. In the illustrated embodiment, the notches have a substantially U-shaped cross-section as illustrated in FIGS. 1, 6 and 7. However, other embodiments may employ other notch shapes such as V-shapes, semi-circular shapes, or other desired shapes. Also, the separation features may extend upwardly towards the flange as opposed downwardly away from the flange as illustrated in FIGS. 1, 6 and 7. For example, some embodiments may include a truncated pyramid extending up (towards the flange) from a valley or a peak.

FIGS. 6 and 7 illustrate a cross-section of a stack of trays which passes through a wall with two notches formed therein. Using this type of separation feature, a positive draft angle may be applied thereby alleviating some of the manufacturing problems associated with de-nesting lugs having a negative draft angle.

FIG. 2 illustrates a second tray 200 having a contour designed to hold an item. The contour is substantially the same as that of tray 100. The tray 200 may be manufactured from Polyethylene Terephthalate (PETE), Polyethylene Terephthalate Glycol copolymer (PETG), Amorphous Polyethylene Terephthalate (APET), or other plastic materials. The tray 200 may be manufactured using a thermoforming process as generally described with respect to tray 100.

The contour of tray 200 includes a series of peaks 210 and valleys 220 of differing heights (and depths) that create pockets configured to receive an item. The relative height difference between the peaks 210 and valleys 220 can create walls 230 within the contour to define the item pockets. Some of these walls 230 may also support the item to be placed within the tray 200. The relative location and size of the peaks 210 and valleys 220 defined by the contour of tray 200 is substantially the same as the relative location and size of the peaks 110 and valleys 120 defined by the contour of tray 100 as can be seen in FIGS. 1 and 2.

The illustrated tray 200 also includes a substantially planar flange 240 that extends outwardly around the periphery of the tray 200. In various embodiments, this flange 240 may be used in downstream operations to provide a surface for engagement by a lid or seal (not shown). Other embodiments may not include this flange.

In some embodiments, significant portions of the surface area of the tray 200 are planar (either tops of peaks 210 or bottoms of valleys 220). This type of surface may create adhesion issues if a tray 200 is nested with another tray 200.

Separation features 250 may be formed in some of the peaks 210, valleys 220 and/or walls 230. In the illustrated embodiment, the separation features 250 are notches formed at strategic locations within the walls 230. In the illustrated embodiment, four separation features are formed in the tray. However, other embodiments may have more of less separation features. In the illustrated embodiment, the notches have a substantially U-shaped cross-section as illustrated in FIGS. 2, 6 and 7. However, other embodiments may employ other notch shapes such as V-shapes, semi-circular shapes, or other desired shapes. Also, the separation features may extend upwardly towards the flange as opposed downwardly away from the flange as illustrated in FIGS. 2, 6 and 7. For example, some embodiments may include a truncated pyramid extending up (towards the flange) from a valley or a peak.

FIGS. 6 and 7 illustrate a cross-section of a stack of trays that passes through a wall with two notches formed therein. Using this type of separation feature, a positive draft angle may be applied thereby alleviating some of the manufacturing problems associated with de-nesting lugs having a negative draft angle.

FIGS. 3-7 illustrate an exemplary stack 300 that includes trays 100 and trays 200. As illustrated, trays 100 and trays 200 are alternatively stacked. Each tray is partially nested with an adjacent tray and the trays are prevented from fully nesting as a result of the separation features. As illustrated in FIGS. 6 and 7, the separation features 150 in tray 100 are disposed in a different location relative to the contour than the separation features 250 disposed in tray 200. This can also be seen by comparing tray 100 illustrated in FIG. 1 and tray 200 illustrated in FIG. 2. As a result, the separation features 150, 250 do not nest into separation features of adjacent trays. Instead, they engage a different portion of the adjacent tray thereby preventing complete nesting of the adjacent trays. This reduces the adhesion between the adjacent trays which aids in separation of individual trays in downstream operations. A benefit of this separation is that the adhesion between the trays can be reduced to such a degree that applying a release agent is not required. This can represent a significant improvement in medial device trays where applying a lid to the tray is necessary to maintain sterilization. The amount of separation may be varied based on the relative height of the separation features. In some embodiments, the separation is approximately 10 mm.

FIGS. 3-7 illustrate a stack of trays 300 where the tray “opens” upward. However, it should be understood that the trays may be stacked with the tray “opening” downwardly or to the side as desired.

In the illustrated example, the separation features 150, 250 of trays 100 and tray 200 respectively are substantially the same shape, but are located at different relative positions to create the partial nesting when alternately stacked. In other embodiments, the separation features may have different shapes between the different tray designs (or within the same design). Additionally, there may be more that two different trays designs that are alternately stacked. For example there may be three or more different tray designs (e.g., Tray A, Tray B and Tray C) that are alternatively stacked. Furthermore, the illustrated trays include four separation features per tray design; however, other embodiments may have more or less separation features as desired.

Additionally, the aforementioned overdriven locking de-nesting lug condition can be eliminated with embodiments of the present invention because the separation features in adjacent trays in a stack are not aligned such that they can be driven into engagement with each other by a downward force on the stack. Furthermore, various embodiments of this invention can also eliminate the need for release agents (topical or otherwise) being applied to the trays, and thereby removing a root cause of failed lid seals in medical device trays.

By employing various embodiments of this invention the medical device manufacturing industry may realize a dramatic reduction in operational costs related to quality control, scrap, product liability insurance, manufacturing line efficiencies and other operational areas. Additionally there may be a direct improvement in product safety which could benefit the patients for whom these devices are destined.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

1. A stack of plastic trays comprising: a first tray comprising: a substantially planar flange portion extending around the perimeter of the first tray; a first contour portion inward of the flange portion and configured to receive a product; and a plurality of first separation features formed within the first contour portion and having a positive draft angle; and a second tray comprising: a substantially planar flange portion extending around the perimeter of the second tray; a second contour portion having substantially the same shape as the first contour portion; and a plurality of second separation features disposed within the second contour portion of the second tray and having a positive draft angle; wherein a location of the plurality of second separation features relative to the second contour portion is different from a location of the plurality of first separation features relative to the first contour portion; and wherein further the first tray is disposed on top of the second tray and each one of the plurality of first separation features engages a portion of the second contour portion of the second tray at a location spaced apart from the second separation features formed in the second contour portion thereby spacing apart a bottom surface of the first contour portion of the first tray from the top surface of the second contour portion of the second tray.
 2. The stack of trays of claim 1, wherein the first separation feature is substantially U-shaped.
 3. The stack of trays of claim 1, wherein the first separation feature is a notch formed in a wall defined in the contour of the first tray.
 4. The stack of trays of claim 1, wherein the first tray is constructed from Polyethylene Terephthalate (PETE), Polyethylene Terephthalate Glycol copolymer (PETG), or Amorphous Polyethylene Terephthalate (APET).
 5. A plurality of stacked trays comprising: a first tray having a first contour defining a plurality of walls that at least partially define a pocket to receive a product and a first plurality of separation features formed in at least some of the plurality of walls; and a second tray having a second contour defining a plurality of walls wherein the plurality of walls defined by the second contour have the same relative position as the plurality of walls defined by the first contour, and the second contour further defining a second plurality of separation features formed in at least some of the plurality of walls of the second tray at different relative locations from the first plurality of separation features defined in the first tray; wherein further the first tray is disposed on top of and partially nested within the second tray and each one of the plurality of first separation features engages a portion of the plurality of walls defined by the second contour at a location spaced apart from the second plurality of separation features.
 6. The stack of trays of claim 5, wherein the first separation feature is substantially U-shaped.
 7. The stack of trays of claim 5, wherein the first tray is constructed from Polyethylene Terephthalate (PETE), Polyethylene Terephthalate Glycol copolymer (PETG), or Amorphous Polyethylene Terephthalate (APET).
 8. A method of producing a stack of plastic trays comprising the steps of: forming a first tray having a first contour defining a plurality of walls that at least partially define a pocket to receive a product and a first plurality of separation features formed in at least some of the plurality of walls; forming a second tray having a second contour defining a plurality of walls wherein the plurality of walls defined by the second contour have the same relative position as the plurality of walls defined by the first contour, and the second contour further defining a second plurality of separation features formed in at least some of the plurality of walls of the second tray at different relative locations from the first plurality of separation features defined in the first tray; and disposing a first tray on top of the second tray wherein each one of the plurality of first separation features engages a portion of the plurality of walls defined by the second contour at a location spaced apart from the second plurality of separation features.
 9. The method of claim 8 further comprising the step of disposing a second tray on top of the first tray.
 10. A plurality of stacked trays for use in storing medical devices comprising: a first tray comprising: a substantially planar flange portion extending around the perimeter of the first tray and configured to provide an engagement surface for a lid to seal; a first contour defining a first plurality of walls that at least partially define a pocket to receive a medical device; and a first plurality of separation features formed in at least some of the plurality of walls; and a second tray comprising: a substantially planar flange portion extending around the perimeter of the first tray and configured to provide an engagement surface for a lid to seal; and a second contour defining a second plurality of walls wherein the second plurality of walls have the same relative size and position within the second contour as the first plurality of walls defined by the first contour, and the second contour further defining a second plurality of separation features formed in at least some of the plurality of walls of the second tray at different relative locations from the first plurality of separation features defined in the first tray, wherein further the first tray is disposed on top of and partially nested within the second tray and each one of the plurality of first separation features engages a portion of the plurality of walls defined by the second contour at a location spaced apart from the second plurality of separation features, and wherein the engagement of the first separation features of the second contour spaces apart other bottom surfaces of the first contour from the top surfaces of the second contour thereby minimizing adhesion between the first and second trays in the stack of trays. 